JPH06-002625A published by the Japan Patent Office in 1994 proposes a variable intake device for a spark ignition multi-cylinder internal combustion engine. The variable intake device alternates between inertial charging and resonance charging to improve the charging efficiency of the engine.
The variable intake device comprises a pair of intake collectors, a communication passage connecting the pair of intake collectors, and a control valve unit which opens and closes the communication passage. When the rotation speed of the engine is higher than a threshold, the control valve unit opens the communication passage and the engine aspirates air under an inertial effect of intake air. When the rotation speed of the engine is not higher than the threshold, the control valve unit closes the communication passage and the engine aspirates air under a resonance effect of the pair of isolated intake collectors.
Each of the intake collectors supplies air via branch pipes to engine cylinders in which ignition does not take place successively. The communication passage is formed, for example by molding an aluminum alloy as an independent communication passage structure. The control valve unit is constituted by a butterfly type valve body formed about a valve shaft, and bearing bosses formed on the communication passage structure for supporting the valve shaft so as to be free to rotate.